Number of points in the output window. If zero or less, an empty
array is returned.

at : float

Attenuation (in dB).

sym : bool, optional

When True (default), generates a symmetric window, for use in filter
design.
When False, generates a periodic window, for use in spectral analysis.

Returns:

w : ndarray

The window, with the maximum value always normalized to 1

Notes

This window optimizes for the narrowest main lobe width for a given order
M and sidelobe equiripple attenuation at, using Chebyshev
polynomials. It was originally developed by Dolph to optimize the
directionality of radio antenna arrays.

Unlike most windows, the Dolph-Chebyshev is defined in terms of its
frequency response: